Submarines and other types of military ships are examples of marine vessels that are subject to shock impacts such as, for example, those generated by energy from nearby explosions. Shock testing and qualification is essential to the certification process of critical equipment installed in such vessels. To ensure a level of resistance to damage resulting from shock-induced loadings, shock qualification testing must adequately simulate environment and input forces resulting in shock impacts exerted on the ship.
Testing requirements for equipment installed in such vessels are determined by their orientation, location and method of attachment to the ships structure. Class I equipment must meet specific shock test requirements when installed, without the use of resilient mounting hardware between the device and the ship's structure. Class II equipment is required to meet MIL-S-901 standards for shock resistance, but can do so with the use of resilient mounting parts when installed in its proper shipboard position when applicable.
Currently, shock qualification testing of Class II medium weight (i.e., 500-4500 lb) equipment typical to military seaworthy vessels requires underwater explosion (“UNDEX”) testing utilizing a Floating Shock Platform (FSP), which simulates a marine vessel such as a submarine or other type of ship. This corresponds to the Heavyweight test category of MIL-S-901 (“Heavyweight test”). A Unit Under Test (UUT), which is a particular piece or pieces of equipment or simulated representation thereof, is mounted on the FSP in the same or comparable manner as it would be on an actual vessel on which it would be installed. The Heavyweight test subjects the FSP to a shock impact by a nearby underwater explosive charge. The FSP deck frequency and the underwater explosive charge size and depth are jointly configured to exhibit the desired frequency response and magnitude of the shock impact imparted on the FSP by the explosive charge.
Conducting a Heavyweight test utilizing a FSP is substantially more expensive than associated test of equipment on a Medium Weight Shock Machine (MWSM). The cost savings from the MWSM result from it being performed in a readily accessible and controlled environment on a laboratory test apparatus. The logistics and safety issues associated with Heavyweight testing are significantly increased compared to MWSM testing. It is not currently permissible to test Class II medium weight equipment using a MWSM because there is no existing MWSM fixture/method that adequately simulates the required dynamic environment when testing on the MWSM. As a result, medium weight Class II equipment has to be shock tested on FSPs that is substantially more expensive and schedule intensive than testing on a MWSM. Testing on a MWSM is on average at least five times less expensive than a Heavyweight test using a FSP.
Although much of the medium weight Class II equipment is light enough to be mounted in a MWSM, a technology, technique, or fixture does not currently exist that sufficiently replicates the environment seen during a FSP shock event. Therefore, an apparatus and associated method of operation that allows medium weight Class II equipment to be tested on a MWSM in a manner that adequately simulates the required dynamic response exhibited when subjected to Heavyweight test utilizing a FSP would be advantageous, desirable and useful.